1. Field of the Invention
The present invention relates generally to the fields of immunology and neurobiology and also relates generally to the study of multiple sclerosis. More specifically, the present invention relates to an active factor present in homogenized brain tissue which inhibits antigen-driven proliferation of lymphocytes in culture, but stimulates proliferation in response to most mitogens.
2. Description of the Related Art
The brain has long been considered an immune-privileged site, along with the eye, the gravid uterus, and the testis [1, 2]. Immune privilege is probably due to active immune regulation in the privileged site rather than isolation of the privileged site from the immune system and probably results from the combined effects of multiple regulatory mechanisms. Mechanisms which contribute to immune regulation in the eye include soluble immunosuppressive factors and possibly the constitutive expression of Fas ligand [3, 4]. These mechanisms may also be operative in the brain [5, 6]. Gangliosides may also regulate immune responses in the brain [7]. There are probably several other mechanisms as well.
One possible immunoregulatory agent which has received little attention is the parenchymal microenvironment. The effector phase of immune responses occurs at least in part in the tissues, and the effector cells are in intimate contact with the extracellular matrix and the extracellular surfaces of parenchymal cells. It is reasonable to expect that molecules present in the extracellular environment could convey regulatory signals to immune effector cells through interaction of the molecules present in the extracellular space with specific receptors on immune cells. A normal extracellular environment might inhibit immune responses, while an extracellular environment altered by the effects of infectious organisms might promote immune responses [8]. The extracellular environment in immune privileged sites such as the brain might have unique regulatory effects.
The prior art is deficient in the lack of the identification of the factors responsible for the inhibition of immune function in the brain. The present invention fulfills this longstanding need and desire in the art.
The current invention comprises a brain homogenate which inhibits the proliferation of lymphocytes resulting from stimulation with antigens such as chicken ovalbumin (OVA) and the purified protein derivative (PPD) of Mycobacterium tuberculosis. This inhibition appears to involve the blocking of the stimulatory effect of IL-2 on the proliferation of the antigen-stimulate lymphocytes
The brain homogenate can also be used to affect mitogen stimulated lymphocyte proliferation. With most mitogens, including concanavalin A (ConA), lipopolysaccharide (LPS), and anti-CD3 antibody, the brain homogenate enhances the mitogen stimulated proliferation of the lymphocytes. One exception is the mitogen mixture ionomycin with phorbol 12-myristate 13-acetate (PMA), where the brain homogenate suppresses the mitogen induced proliferation of the lymphocytes
The current invention also comprises an active factor present in the brain homogenate which has been demonstrated to contain most of activity of the homogenate with respect to the lymphocyte proliferation. The active factor is part of a particulate complex which forms a sediment at 14,000 g and is heat and formalin stable. The active factor contains terminal sialic acid residues and is inactivated by digestion with trypsin or proteinase K but not with hyaluronidase.
The active factor can be partially isolated from the brain homogenate by centrifugation, solubilization in alkali, and partial purification on a SUPEROSE(trademark) 6HR 10/30 sepharose gel filtration column equilibrated with 0.04 N NaOH, where the factor elutes in the void volume.
The present invention also comprises a pharmaceutical composition which can be used to treat pathophysiological states characterized by undesired activity of the immune system. Possible uses include the treatment of various autoimmune diseases including multiple sclerosis.